The present invention relates to solid polyelectrolyte fuel cells and, in particular, to a structure of an electrode-membrane-frame assembly for fuel cells as well as a manufacturing method therefor.
The solid polyelectrolyte fuel cell (hereinafter, occasionally referred to as “PEFC”) is a device for concurrently generating electric power and heat by electrochemically reacting a hydrogen-containing fuel gas with an oxygen-containing oxidizer gas such as air.
The most typical solid polyelectrolyte fuel cell comprises a polyelectrolyte membrane supported by a frame body with a gas-sealing gasket provided in a peripheral edge portion of the frame body, a membrane-electrode assembly (MEA) made up with an anode bonded to one surface of the electrolyte membrane and with a cathode bonded to the other surface of the electrolyte membrane, and an anode-side conductive separator plate and a cathode-side conductive separator plate with the MEA sandwiched therebetween. Gas feeding parts for feeding fuel gas and oxidizer gas to the anode and the cathode, respectively, are formed at peripheral edges of central portions of separator plates to be put into contact with the MEA.
A structure of such a conventional solid polyelectrolyte fuel cell is disclosed, for example, in Patent Document 1. Specifically, as shown in FIG. 14, an MEA 303 whose peripheral edge portion is supported inside a frame body 300 is sandwiched by separators 301 is disclosed.
Such an MEA is incorporated at a thicknesswise generally center of the frame body. As a bonding method therefor, adhesive or mechanical clamping or the like is adopted.    Patent Document 1: JP 2005-100970 A    Patent Document 2: WO 2006/040994
However, the bonding method with adhesive for a polyelectrolyte membrane may incur performance deterioration of the polyelectrolyte membrane due to volatile components of the adhesive and so its applicable conditions are limited. Also, the bonding method by mechanical clamp causes a problem that crossleak tends to occur through a minute gap between the polyelectrolyte membrane and the frame body. The crossleak phenomenon refers to a phenomenon that with reference to FIG. 14, part of gas fed into the cell passes through a slight gap generated between an inner edge of the frame body 300 and an electrode 302 so that the gas leaks from one of the anode or cathode side to the other. For improvement of power generating efficiency in fuel cells, there is a need for reducing such crossleaks.
As one method for suppressing occurrence of such a crossleak phenomenon, it is conceivable to form the frame body by injection molding so that the peripheral edge portion of the MEA is placed inside the frame body. Using such a method makes it possible to improve close contactability between the frame body and the peripheral edge portion of the MEA and thereby reduce the crossleak. Such a method is disclosed also in, for example, Patent Document 2.
Specifically, as shown in FIG. 15A, a first frame member 311 preliminarily formed into a frame shape by injection molding or the like is prepared. Then, as shown in FIG. 15B, a peripheral edge portion of an electrode 314 in which anode and cathode are placed on both sides of an electrolyte membrane 313, i.e., a peripheral edge portion 313a of the electrolyte membrane 313 is positioned and set on the first frame member 311. Thereafter, as shown in FIG. 15C, a resin material is injected by injection molding onto the top of the first frame member 311 with the peripheral edge portion 313a of the electrolyte membrane 313 set thereon, by which a second frame member 312 is formed. By forming the second frame member 312 integrally bonded to the first frame member 311 by injection molding as shown above, the peripheral edge portion 313a of the electrolyte membrane 313 sandwiched therebetween can be retained in an even closer contact state.
However, such a formation method by injection molding has the following issues. As shown in FIG. 16A, during the formation of the second frame member 312 by injection molding, when a high-temperature, high-pressure resin material P is injected into a metal mold (not shown), the peripheral edge portion 313a of the electrolyte membrane 313 placed on top of the first frame member 311 may be floated up in the resin material due to flow resistance of the resin material P, resulting in some cases in a state of being peeled up from the top surface of the first frame member 311. If the resin material P is solidified in such a state, the electrode 314 is retained with the peripheral edge portion 313a of the electrolyte membrane 313 completely floated up inside the second frame member 312 as shown in FIG. 16B.
In such a case, it can occur that the electrode 314 cannot be retained enough by the frame body 310 or that the electrolyte membrane 313 may be damaged, so that the crossleak cannot be reduced enough. In particular, the MEA is a comparatively expensive member, and implementation of high yield (productivity) is desired in the manufacture of fuel cells. Further, together with such productivity improvement in the fuel cell manufacture, improvement in performance of fuel cells such as power generating efficiency also has still been being demanded.
Accordingly, a first object of the present invention, lying in solving the above-described issues, is to provide an electrode-membrane-frame assembly for solid polyelectrolyte fuel cells, as well as a manufacturing method for the electrode-membrane-frame assembly and a solid polyelectrolyte fuel cell including the electrode-membrane-frame assembly, the electrode-membrane-frame assembly being capable of effectively suppressing the crossleak phenomenon between the polyelectrolyte membrane and the frame body and allowing high yield to be implemented in its manufacture.
A second object of the invention is to provide an electrode-membrane-frame assembly for fuel cells which allows the performance such as power generating efficiency to be improved in solid polyelectrolyte fuel cells, as well as to provide a manufacturing method for the electrode-membrane-frame assembly and a polyelectrolyte fuel cell including the electrode-membrane-frame assembly.